In a conventional inkjet printer, a printhead has a series of actuators which ejects printing fluid or ink out of an actuator nozzle and onto an image receiving substrate. The ink drop mass, size, and drop velocity can influence the quality of the printing. Further, a variation in drop speed across the series of actuators can affect the quality of the printing, as drop speed variation can lead to poor image quality.
Conventional piezoelectric inkjet printheads mainly rely on two part processes for jetting: first, ink is drawn into an actuator chamber when a piezoelectric actuator shrinks; and second, the ink is ejected from the actuator chamber through the actuator nozzle when the piezoelectric actuator expands. The shrinking and expanding is achieved by applying an amplified waveform to the actuator.
During the printing process, droplets of ink can collect on the external surface of the printhead faceplate. Additionally, more volatile ink components can evaporate, particularly at elevated temperatures, which can result in ink residue such as ink pigment collecting around the nozzle which can eventually partially or completely plug the actuator nozzle. Furthermore, the residue can form an ink-attractive layer that causes ink to drool from the actuator nozzle during printing. These can adversely affect the printing quality, such as the ink drop mass, velocity, trajectory, and robustness.
To remove the ink droplets from the printhead faceplate surface and the residue from the nozzle, printhead maintenance can be performed. During printhead maintenance, a positive pressure of several psi can be applied to the printhead reservoir, which pushes ink mixed with air bubbles out from the actuator nozzle. Most of the purged ink runs off the printhead because of an anti-wetting coating on the faceplate surface, and only some tiny ink droplets may scatter on the faceplate surface. Then a fluorosilicone blade wiper can be placed against printhead faceplate. The wiper slowly moves from the top to the bottom of faceplate to clean the ink droplets from the faceplate surface.
As ink formulations change and improve, other methods of printhead maintenance are needed.